A Great Online Textbook
Okay, so I found another online textbook (see entry below). This one is fantastic as it has both Prehistory - 1500 and 1500 to the present. Each course is broken down into the normal textbook categories. There are also great links which vary depending on the time period. The only glaring omission is lots of pictures, but if you wanted to save on a real textbook or need one for students to work on at home, then this resource might be the answer.